The DC fan without bushing has been well known to equip various bearings between fan and fan housing in order to enhance rotation and diminish noise for fan. For example, a ball bearing or an oily bearing (or called self-lubricating bearing) is commonly applied. It has been well known that the oily bearing possesses porous structure made by sintering copper alloy or iron alloy so as to absorb lubricant. However, the lubricant will be forced to sputter due to centrifugal effect to contaminate entire fan housing when the fan shaft in the oily bearing rapidly rotates, and the oil-retaining quantity of oily bearing reduces. Therefore, when the fan is used too long, the lubricating efficiency of bearing becomes bad gradually and noise of bearing becomes loud gradually, even the fan will stop rotating.
It has been well known that a conventional method for preventing losing oily bearing lubricant is to set an oil-retaining ring (or called washer, pad or oil ring) at an end or two ends of the oily bearing. For example, in R.O.C. Taiwan Patent No. 390548 “oil-recovering structure for self-lubricating bearing of a small-sized motor”, a washer is set on an end surface of self-lubricating bearing so as to prevent lubricant from spilling. Also, at least a groove is set on the radial surface of self-lubricating bearing, extends to the end surface of self-lubricating bearing, and penetrates to an axis hole. Therefore, although it is unavoidable that the lubricant is sucked out of the self-lubricating bearing by the centrifugal force when a fan shaft rotates, the lubricant flows along the end surface of self-lubricating bearing and the groove of radial surface of self-lubricating bearing while obstructed by the washer, and gradually returns to the self-lubricating bearing. The foregoing oil recovery system is called external-recycle, which is that the lubricant is driven to flow from the axis hole of self-lubricating bearing through the end surface to the radial surface of self-lubricating bearing to distribute over the whole radial surface of the self-lubricating bearing. Then, the high losing rate of lubricant increases the improper loss of lubricant and the risk of fan housing, also the lubricant is turned into muddy oil to slow the rotating speed of fan due to the dust caused by friction of each part.
Another known self-lubricating bearing for DC micro fan without bushing has been disclosed in R.O.C. Patent No. 355037 “improvement of lubricating structure for DC fan bearing without bushing”, which is to equip an oil-storing trench at an adequate location inside a pivoting hole (or called axis hole) of self-lubricating bearing as an oil-retaining area. A plurality of recess trenches are set on a pivoting base of a fan housing (i.e. outside the radial surface of self-lubricating bearing) to form an oil-storing area and an oil-retaining cover (i.e. oil-retaining ring) is set on an end surface of oily bearing corresponding to a fan shaft. Therefore, when the fan rotates a lubricant is still driven to flow from the oil-storing trench to the pivoting base recess trench on the fan housing outside the oily bearing, then, an external-recycle oil-recovery system is formed. However, the oil-retaining cover only can decrease overflow of lubricant, although the self-lubricating bearing is surface pivoted to the pivoting base of the fan housing, it still cannot obstruct overflow of lubricant and the lubricant leaks at the bottom of pivoting surface so that the oil-retaining ability is not improved efficiently.